Preheat oven to directions on back of cake mix. Mix all ingredients until combined, 2 minutes. Spoon into bundt cake pan and let cook to directions on back of package. Let cake cool on wired rack for 10 minutes then take cake out of the pan and on the wire rack to cool completely.
Cherry Syrup:
While cake is cooking, make the syrup by placing all ingredients in a sauce pan over medium heat. Bring to a simmer and simmer for 10 minutes.
Take off the heat and pour mixture through a fine mesh colander gently crushing the cherries to get as much juice out as your can. Will make about 1/2 Cup of liquid, place in fridge until ready to assemble cake.
Dr. Pepper Frosting:
Place the Dr. Pepper in a pan on the stove and boil to reduce the liquid until only 1/2 Cup remains. This will take 25-30 minutes on high. Let cool completely before making the frosting.
Cream the butter in a bowl and slowly add in the powdered sugar. When all the sugar is incorporated, add in the vanilla and whip on high for 4 minutes. Add in the Dr. Pepper very carefully on low speed. Set aside.
Cake Assembly:
Carefully cut the cake into three layers. On the first layer, brush on the cherry syrup to your taste, you will need a little more than you think. Let it soak in this will keep the cake extra moist and add more cherry/Dr. Pepper kick. Using a piping bag or spatula, frost the cake layer, trying to make sure the outside will look pretty. Place the second cake layer on top, add more cherry syrup. Add another layer of the frosting. Add the top layer of cake and if desired, design with the frosting as you wish, top with cherries for garnish and chocolate shavings.
Serve and enjoy!
Notes
The recipe for cherry syrup makes more than is needed. Keep it to add an extra kick to cocktails, for another cake or over ice cream!